writeback: Do not sort b_io list only because of block device inode

It is very likely that block device inode will be part of BDI dirty list
as well. However it doesn't make sence to sort inodes on the b_io list
just because of this inode (as it contains buffers all over the device
anyway). So save some CPU cycles which is valuable since we hold relatively
contented wb->list_lock.

Signed-off-by: Jan Kara <jack@suse.cz>

2 files changed, 6 insertions, 4 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2091db8cdd78..256233098206 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -606,7 +606,7 @@ static struct block_device *bd_acquire(struct inode *inode)
         return bdev;
 }
 
-static inline int sb_is_blkdev_sb(struct super_block *sb)
+int sb_is_blkdev_sb(struct super_block *sb)
 {
         return sb == blockdev_superblock;
 }
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 3be57189efd5..cabdece4cb39 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -68,7 +68,7 @@ static inline struct backing_dev_info *inode_to_bdi(struct inode *inode)
 {
         struct super_block *sb = inode->i_sb;
 
-        if (strcmp(sb->s_type->name, "bdev") == 0)
+        if (sb_is_blkdev_sb(sb))
                 return inode->i_mapping->backing_dev_info;
 
         return sb->s_bdi;
@@ -250,11 +250,13 @@ static int move_expired_inodes(struct list_head *delaying_queue,
                 if (work->older_than_this &&
                     inode_dirtied_after(inode, *work->older_than_this))
                         break;
+                list_move(&inode->i_wb_list, &tmp);
+                moved++;
+                if (sb_is_blkdev_sb(inode->i_sb))
+                        continue;
                 if (sb && sb != inode->i_sb)
                         do_sb_sort = 1;
                 sb = inode->i_sb;
-                list_move(&inode->i_wb_list, &tmp);
-                moved++;
         }
 
         /* just one sb in list, splice to dispatch_queue and we're done */